But internal clashes about the government insurance option have begun to spill into the open — as Sen. John Rockefeller (D-W.Va.) has gone public with his case against consumer-owned health care cooperatives, which are viewed as a compromise between progressives who want a public competitor to private insurers and Republicans who don’t want a new government plan.

“I will be darned if I support or allow to move forward — to the extent that I can make a noise about it — something which sounds user-friendly,” Rockefeller said in an interview. “What I have to worry about is, are co-ops going to be effective taking on these gigantic insurance companies? And from everything I know from people who represent them, the answer is a flat ‘no.’”

With four of five congressional committees having endorsed health care bills with a public plan, the focus now turns to the Finance Committee, where debate on the issue has been heated and mostly private up until now.

It’s the only committee proposing a private-sector insurance cooperative, rather than a government-run plan, as a mechanism to hold private insurers accountable. But the passage Friday of a House Energy and Commerce Committee bill with a strong public plan puts another squeeze on the odd man out, the Finance Committee.

“They may be right,” said Sen. Kent Conrad (D-N.D.), who proposed the co-op model because he believes the public plan cannot clear the Senate. “I have seen no evidence that changes the vote count in the Senate.”

As Congress attempts to overhaul health care, the public plan debate has been among the most volatile, noisy and expensive.

Early last week, progressives thought their top priority looked dim. President Barack Obama told Time magazine that a co-op could meet his definition of a public plan. Senate Majority Leader Harry Reid (D-Nev.) said his main responsibility was getting legislation that could pick up 60 votes and thwart a filibuster, which the public plan is unlikely to do. And liberal House Democrats revolted over a deal with conservative Democrats to weaken the new government insurance plan.

By Friday, though, public plan advocates were suddenly feeling pretty good. They didn’t get exactly what they wanted in the Energy and Commerce Committee bill — their first preference was a government-run plan tied to Medicare rates rather than negotiated rates — but they had strengthened their hand against the Finance Committee.

“There will be a backstop,” said a Democratic Senate official, who spoke on the condition of anonymity to discuss strategy. “It ensured that whatever happens in the Senate Finance Committee, there will be something of a firewall in the conference. The House will be an equal partner in the conference, and they will be united in presenting a pretty viable, strong public option and one of the two committees marking up in the Senate will have done the same.”

Rep. Eliot Engel (D-N.Y.) called the inclusion of the public plan “a line in the sand.”

“We’re trying to provide health care to 47 million uninsured people,” Engel said. “I believe the way to help them is to have a robust public option with plans tied to Medicare.”

The Finance Committee leans moderate to conservative. There are only a handful of Democrats who might go to the mat for the public option, including Rockefeller, Sens. Chuck Schumer of New York, Debbie Stabenow of Michigan, John Kerry of Massachusetts and Robert Menendez of New Jersey.

It’s too early to tell whether the liberal committee members would vote against a bill with a co-op option. They will look at the whole package for affordability measures and make a judgment, aides said. But since Baucus is negotiating with three Republicans, he could lose a few Democrats and still push a bill through his committee.

Rockefeller has sparred privately with Conrad and Baucus during their Democrat-only Finance Committee meetings about what Rockefeller views as a disregard for measures that would make insurance truly affordable to the poor in West Virginia. But when Rockefeller emerged from those meetings, he tended to deliver only cryptic statements to the media.

On Thursday, however, he stopped putting on a polite face. In a warning shot of sorts, he sent letters to the Government Accountability Office, the National Cooperative Business Association and the Agriculture Department, asking dozens of questions about the history, success rate and legal, regulatory and licensure requirements of cooperatives — questions he said he has yet to receive answers from by the committee.

“I don’t think he is very happy with me, and I regret that,” Rockefeller said of Conrad. “I can’t worry about that.”

Rockefeller said he started looking into health cooperatives and found there are about 20 in the country, but only two with a strong track record — Group Health Cooperative of Washington state and HealthPartners of Minneapolis.

“If you are going to fight the insurance industry with a system that might fail, I sort of feel an obligation to know about that and to learn about that,” Rockefeller said. “I can’t vote now or later for something in which the big insurance companies are going to beat the tar out of what are totally nonexistent health care co-ops.”

Conrad said Rockefeller is missing a big point: The cooperatives would operate in an overhauled health care system with 40 million new entrants in the market and $6 billion in startup funds.

Under the Finance Committee proposal, co-ops could form on the state, regional and national level. If one state lacks a co-op, adjoining states could move in and offer one. There could be a national co-op as well, but it would need to be licensed in every state, Conrad said.

“There are not the votes for the public option in the U.S. Senate,” Conrad said in an interview Saturday. “My grandmother said you can curse the darkness, or light the candle. You can wish and hope and push for something that according to every vote count will not get enough votes in the U.S. Senate. That was the reason I was asked to come up with the alternative.”

But if the fight in the House last week is any indication, public plan proponents in the Senate are unlikely to give up easily.

“Of the thousands of issues we address in this legislation, only a handful give us an opportunity to make real progress,” said Rep. Anna Eshoo (D-Calif.) a member of the Energy and Commerce Committee who pushed to protect the public plan. “This is one of them.”

If the co-op makes it through the Finance Committee, it would likely to set up a colossal lobbying war when Reid merges the bill with one approved by the Senate health committee, which approved a public plan similar to one in the House bill.

At some point, one side is going to have to give in — or walk, forcing Democratic congressional leaders to use a procedural maneuver known as reconciliation. It would allow Democrats to pass a bill in the Senate with a simple majority, rather than with the 60-vote, filibuster-proof threshold.

“If it is a choice between getting a good health care bill and doing it in reconciliation, I will take that in a shot,” Rockefeller said. “What I don’t like is no result. And if it takes more time to get a result — even if has to be done through reconciliation as a last resort — don’t think I am going to lose sleep over that.”